The single agent efficacy of selective mutant BRAF inhibitors in patients with advanced melanoma is a transformative advance but the uniformly short-lived responses have now defined therapeutic resistance as the central paramount question in the field. While much of the field is focusing on somatic alterations in the melanoma cells that can drive resistance, we hypothesize that the tumor microenvironment plays an active contributory role in dictating the response to therapy initially and in facilitating emergence of resistance over time, hence modulating tumor-stromal alterations together with targeted therapy is a rational combination strategy to minimize emergence of resistance. To address this systematically, we have brought together this U54 team with diverse but complementary expertise in clinical, translational and basic research in areas of melanoma biology and genetics, immunology and cancer genomics to pursue the following two highly inter dependent and interrelated projects. Project 1: Identification of resistance-conferring stromal alterations i BRAF mutant melanoma. Here, global unbiased profiling on transcriptomic, epigenomic and proteomic levels in BRAF mutant human melanomas and derivative cells at baseline, post-treatment and upon relapse on selective BRAF inhibitor, compared with similar analyses in genetically engineered mouse models, will identify candidate stromal alterations associated with resistance that are dependent on tumor stromal interactions. Functional relevance of these candidates will be validated through genetic or pharmacological perturbation in vitro and in vivo while human relevance will be confirmed through analysis of larger cohort of human samples. Finally, mechanism of action will be explored to support possible strategy of modulating such stromal components to minimize resistance. Project 2: Roles of immune regulatory pathways in resistance to BRAF targeted therapy. Clinical efficacy of immune-inhibitory pathway blockade in human melanoma, supported by preliminary data in human and mouse, has pointed to an active role for immunosuppression in melanoma pathogenesis. This project will study the roles of immune regulatory pathways (through molecules such as CTLA4 and PD-L1) in melanoma and explore the consequences of such modulation on therapeutic response. The two Shared Resource Cores on "Clinically annotated human melanoma for TMEN research" and "GEM models for TMEN research" will not only support activities of these two projects but are expected to be high impact enablers for the entire research network. Finally, this U54 team brings to TMEN a diverse set of unique capabilities that can be leveraged for studies of the tumor microenvironment Thus, in addition to ensuring close interaction and coordination of complementary activities within this center, the 'Administrative Core'will also be responsible for efficient and effective communication and interaction with the TMEN research network.